Adhesive for circuit connection, circuit connection method using the same, and circuit connected structure

ABSTRACT

There are provided an adhesive for connecting a circuit to be interposed between substrates having circuit electrodes thereon opposed to each other and to electrically connect the circuit electrodes on the substrates opposed to each other to the pressurizing direction under pressure, wherein the adhesive contains a compound having an acid equivalent of 5 to 500 KOH mg/g, and an adhesive for connecting a circuit to be interposed between substrates having circuit electrodes opposed to each other and to electrically connect the electrodes on the substrate opposed to each other to the pressurizing direction under pressure, wherein the adhesive comprises a first adhesive layer and a second adhesive layer, and a glass transition temperature of the first adhesive layer after pressure connection is higher than the glass transition temperature of the second adhesive layer after pressure connection.

This application is a Divisional application of prior application Ser.No. 11/723,644, filed Mar. 21, 2007, now abandoned, which is aDivisional application of application Ser. No. 10/258,548, filed Oct.25, 2002, now U.S. Pat. No. 7,208,105 the contents of which areincorporated herein by reference in their entirety. Ser. No. 10/258,548is a National Stage Application, filed under 35 USC 371, ofInternational (PCT) Application No. PCT/JP01/03547, filed Apr. 25, 2001.

TECHNICAL FIELD

This invention relates to an adhesive for connecting circuit, and acircuit connecting method and a circuit connected structure using thesame.

PRIOR ART

For connecting a liquid crystal display and TCP or FPC, or TCP or FPCand a printed wiring board, an anisotropic conductive adhesive in whichconductive particles had been dispersed in an adhesive have heretoforebeen used. Also, in recent years, when a semiconductor silicon chip ismounted on a substrate, without using the conventional wire bonding, theso-called flip chip mounted technology in which a semiconductor siliconchip is directly mounted to the substrate by face down, and applicationof an anisotropic conductive adhesive has been started (JapaneseProvisional Patent Publications No. 120436/1984, No. 191228/1985, No.251787/1989 and No. 90237/1995).

However, the conventional anisotropic conductive adhesive isinsufficient in adhesive force to respective kinds of substrates andsufficient connection reliability cannot be obtained. In particular, toreduce damage or dimensional error to the substrate at the time ofconnection or to improve manufacturing efficiency, lowering in aconnection temperature or shortening of a connection time is requiredbut a sufficient reliability has not yet been obtained.

The present invention is to provide an adhesive for connecting a circuitwhich accomplishes low temperature connecting and shortening of aconnection time, a circuit connecting method using the same and acircuit connecting structure using the same.

SUMMARY OF THE INVENTION

A first embodiment of the present invention relates to (1) an adhesivefor connecting a circuit which is to be interposed between substrateshaving circuit electrodes thereon opposed to each other and toelectrically connect the circuit electrodes on the substrates opposed toeach other to the pressurizing direction under pressure, wherein saidadhesive contains a compound having an acid equivalent of 5 to 500 (KOHmg/g).

(2) There is provided an adhesive for connecting a circuit described inthe above (1), wherein the compound having an acid equivalent of 5 to500 (KOH mg/g) is a compound having at least one carboxyl group.

(3) There is also provided an adhesive for connecting a circuitdescribed in the above (1) or (2), wherein the adhesive further containsa radical polymerizable substance.

(4) There is also provided an adhesive for connecting a circuitdescribed in any of the above (1) to (3), wherein the adhesive furthercontains conductive particles.

(5) There is provided a circuit connecting structure which is a circuitconnecting structure to be interposed between substrates having circuitelectrodes opposed to each other and to electrically connect theelectrodes on the substrate opposed to each other to the pressurizingdirection under pressure, wherein the adhesive for connecting a circuitis an adhesive described in any one of the above (1) to (4).

A second embodiment of the present invention is (6) an adhesive forconnecting a circuit to be interposed between substrates having circuitelectrodes opposed to each other and to electrically connect theelectrodes on the substrate opposed to each other to the pressurizingdirection under pressure, wherein said adhesive comprises a firstadhesive layer and a second adhesive layer, and a glass transitiontemperature (Tg) of the first adhesive layer after pressure connectionis higher than the Tg of the second adhesive layer after pressureconnection.

(7) There is provided an adhesive for connecting a circuit described inthe above (6), wherein Tg of the first adhesive layer after connectionis 50 to 200° C., Tg of the second adhesive layer after connection is 40to 100° C., and Tg of the first adhesive layer is not lower than 5° C.of Tg of the second adhesive layer after connection.

(8) There is provided an adhesive for connecting a circuit described inthe above (6) or (7), wherein conductive particles are contained in atleast one of the first adhesive layer and the second adhesive layer.

(9) There is provided an adhesive for connecting a circuit described inany of the above (6) to (8), wherein a radical polymerizable substanceis contained in at least one of the first adhesive layer and the secondadhesive layer.

(10) There is provided an adhesive for connecting a circuit described inany of the above (6) to (9), wherein a ratio of the thicknesses of thefirst adhesive layer and the second adhesive layer is a thickness of thefirst adhesive layer/a thickness of the second adhesive layer=0.3 to3.0.

(11) There is provided an adhesive for connecting a circuit described inany of the above (6) to (10), wherein a compound having an acidequivalent of 5 to 500 (KOH mg/g) is contained in at least one of thefirst adhesive layer and the second adhesive layer.

(12) There is provided a circuit connecting method which comprisesinterposing the adhesive for connecting a circuit described in any ofthe above (6) to (11) between substrates having circuit electrodesopposed to each other and electrically connecting the electrodes to thepressurizing direction by pressurizing the substrates, wherein saidadhesive comprises a first adhesive layer and a second adhesive layer,Tg of the first adhesive layer after pressure connection is higher thanTg of the second adhesive layer after pressure connection, and the firstadhesive layer having a higher Tg is provided and connected to thesubstrate side having higher modulus of elasticity among the substrateshaving circuit electrode opposed to each other.

(13) There is provided a connecting structure which comprises theadhesive for connecting a circuit described in any of the above (6) to(11) being interposed between substrates having circuit electrodesopposed to each other and the electrodes being electrically connected tothe pressurizing direction by pressurizing the substrates, wherein saidadhesive comprises a first adhesive layer and a second adhesive layer,Tg of the first adhesive layer after pressure connection is higher thanTg of the second adhesive layer after pressure connection, and the firstadhesive layer having a higher Tg is provided and connected to thesubstrate side having higher modulus of elasticity among the substrateshaving circuit electrode opposed to each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the adhesive for connecting a circuit of the present invention, and acircuit connecting method and a circuit connecting structure of thesame, no lifting (delamination) from the substrate or peeling isgenerated after various reliability tests such as humidity resistancetest or heat cycle test, etc., so that no lowering in an adhesive forceor increase in connection resistance occurs whereby excellent connectionreliability is shown.

In the first embodiment of the present invention, a compound having anacid equivalent measured by a titration method using potassium hydroxidein the range of 5 to 500 (KOH mg/g) can be used, and particularly, acompound having at least one carboxyl group is preferably used. If theacid equivalent is less than 5, improvement in adhesive force cannot beobserved, while if it becomes large exceeding 500, water absorption rateof the adhesive becomes large so that reliability of humidity resistanceis lowered. The carboxyl group-containing compound is not particularlylimited so long as it is a compound having a carboxyl group in themolecule. Also, there is no specific limitation in a weight averagemolecular weight (Mw), and a compound having Mw of less than 1,000,000is preferably used. If the molecular weight (Mw) becomes 1,000,000 ormore, flowability of the adhesive lowers. Specific examples of thecarboxyl group-containing compound as a copolymerizable compound may bementioned a carboxylic acid such as oxalic acid, malonic acid, etc.; anda compound in which a carboxyl group is introduced into a polymer suchas polybutadiene, polyvinyl butyral, (meth)acrylic resin, polyimide,polyamide, polystyrene, polyvinyl formal resin, polyester resin, xyleneresin, phenoxy resin, polyurethane resin, urea resin, etc. When acarboxyl group is introduced into a polymer, a carboxyl group-containingcompound may be used or a carboxyl group may be introduced aftersynthesizing the polymer. As a formulation amount of the compound inwhich a carboxyl group is introduced into the polymer to be used in thepresent invention, it is preferably 1 to 80% by weight, particularlypreferably 5 to 70% by weight. If it is less than 1% by weight,adhesiveness becomes poor while if it exceeds 80% by weight, flowabilitytends to be lowered.

As the material other than the carboxyl group-containing compound to beused in the present invention, there may be preferably used athermoplastic resin such as a styrene-butadiene-styrene copolymer,styrene-isoprene-styrene copolymer, etc.; a thermosetting resin such asan epoxy resin, (meth)acrylic resin, maleimide resin, citraconimideresin, nadiimide resin, phenol resin, etc., and a thermosetting resin ispreferably used in the points of heat resistance and reliability,particularly a radical polymerizable material using (meth)acrylic acid,maleimide resin, citraconimide resin or nadiimide resin is preferred inthe point of low temperature curing property.

The adhesive for connecting a circuit in the second embodiment of thepresent invention is constituted by a first adhesive layer and a secondadhesive layer, and it is required that Tg of the first adhesive layerafter connection is higher than Tg of the second adhesive layer afterconnection. Tg of the first adhesive layer is preferably 50 to 200° C.,more preferably 60 to 150° C. Also, Tg of the second adhesive layer is40 to 100° C., and Tg of the first adhesive layer is preferably 5° C.higher than Tg of the second adhesive layer after connection,particularly preferably 10° C. higher than the same.

Also, a ratio of the thickness of the first adhesive layer and thesecond adhesive layer is a thickness of the first adhesive layer/athickness of the second adhesive layer=0.3 to 3.0, preferably 0.8 to3.0. If the thickness is out of the range, no lifting from the substrateor peeling is generated after various reliability tests such as humidityresistance test or heat cycle test, etc., so that excellent connectionreliability can hardly be obtained.

Moreover, in the present invention, when circuit electrodes of thesubstrate opposed to each other are electrically connected by using theabove-mentioned two-layered adhesive layers, the first adhesive layerhaving higher Tg is preferably provided to the substrate side having ahigher modulus of elasticity among the substrates.

As the first adhesive layer or the second adhesive layer to be used inthe present invention, the above-mentioned thermoplastic resin or thethermosetting resin is used, and a thermosetting resin is preferablyused in the points of heat resistance and reliability, particularly aradical polymerizable material using (meth)acrylic acid, maleimideresin, citraconimide resin or nadiimide resin is preferred in the pointof low temperature curing property.

As the (meth)acryl resin, those obtained by subjecting (meth)acrylate toradical polymerization are mentioned, and as the (meth)acrylate, theremay be mentioned methyl (meth)acrylate, ethyl(meth)acrylate,isopropyl(meth)acrylate, isobutyl(meth)acrylate, ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, tetramethylene glycol tetra(meth)acrylate,2-hydroxy-1,3-iacryloxypropane,2,2-bis[4-(acryloxymethoxy)phenyl]propane,2,2-bis[4-(acryloxyethoxy)phenyl]propane, dicyclopentenylmeth)acrylate,tricyclodecanyl(meth)acrylate, tris(acrylxyethyl)isocyanurate, urethane(meth)acrylate, etc., which may be used alone or in combination of twoor more. If necessary, a radical polymerization inhibitor such ashydroquinone, methyl ether hydroquinone, etc. may be used within therange which does not impair curability of the product.

Moreover, when a radical polymerizable substance having a phosphatestructure is used, an adhesive force to an inorganic material such asmetal, etc. can be improved. An amount of the radical polymerizablesubstance having a phosphate structure is 0.1 to 10 parts by weight,preferably 0.5 to 5 parts by weight based on the total amount of theadhesive composition. The radical polymerizable substance having aphosphate structure can be obtained as a reaction product of anhydrousphosphoric acid and 2-hydroxyethyl (meth)acrylate. More specifically,there may be mentioned mono(2-methacryloyloxyethyl)acid phosphate,di(2-methacryloyloxyethyl)acid phosphate, etc., which may be used aloneor in combination of two or more.

As the maleimide resin, those having at least one maleimide group in themolecule may be mentioned, and, for example, there may be mentioned,phenylmaleimide, 1-methyl-2,4-bismaleimide benzene,N,N′-m-phenylenebismaleimide, N,N′-p-phenylenebismaleimide,N,N′-4,4-biphenylenebismaleimide,N,N′-4,4-(3,3-dimethylbiphenylene)bismaleimide,N,N′-4,4-(3,3-dimethyldiphenylmethane)bismaleimide,N,N′-4,4-(3,3-diethyldiphenylmethane)bismaleimide,N,N′-4,4-diphenylmethane-bismaleimide,N,N′-4,4-diphenylpropanebismaleimide, N,N′-4,4-diphenyletherbismaleimide, N,N′-4,4-diphenylsulfone bismaleimide,2,2-bis(4-(4-maleimidophenoxy)phenyl)propane,2,2-bis(3-s-butyl-3,4-(4-maleimidophenoxy)phenyl)propane,1,1-bis(4-(4-maleimidophenoxy)phenyl)decane,4,4′-cyclohexylidene-bis(1-(4-maleimidophenoxy)phenyl)-2-cyclohexylbenzene,2,2-bis(4-(4-maleimidophenoxy)phenoxy)hexafluoropropane, etc., which maybe used alone or in combination of two or more.

As the citraconimide resin, there may be mentioned a resin in which acitraconimide compound having at least one citraconimide group in themolecule is polymerized, and as the citraconimide compound, there may bementioned, for example, phenylcitraconimde,1-methyl-2,4-biscitraconimidebenzene, N,N′-m-phenylenebiscitraconimide,N,N′-p-phenylenebis citraconimide, N,N′-4,4-biphenylenebiscitraconimide,N,N′-4,4-(3,3-dimethylbiphenylene)biscitraconimide,N,N′-4,4-(3,3-dimethyldiphenylmethane)biscitraconimide,N,N′-4,4-(3,3-diethyldiphenylmethane)biscitraconimide,N,N′-4,4-diphenylmethanebiscitraconimide,N,N′-4,4-diphenylpropane-biscitraconimide,N,N′-4,4-diphenyletherbiscitraconimide,N,N′-4,4-diphenylsulfonebiscitraconimide,2,2-bis(4-(4-citraconimidophenoxy)phenyl)propane,2,2-bis(3-s-butyl-3,4-(4-citraconimidophenoxy)phenyl)propane,1,1-bis(4-(4-citraconimidophenoxy)phenyl)decane,4,4′-cyclohexylidene-bis(1-(4-citraconimidophenoxy)phenoxy)-2-cyclohexylbenzene,2,2-bis(4-(4-citraconimidophenoxy)phenyl)hexafluoropropane, etc., whichmay be used singly or in combination of two or more in admixture.

As the nadiimide resin, there may be mentioned a resin in which anadiimide compound having at least one nadiimide group in the moleculeis polymerized, and as the nadiimide compound, there may be mentioned,for example, phenylnadiimide, 1-methyl-2,4-bisnadiimidebenzene,N,N′-m-phenylenebisnadiimide, N,N′-p-phenylenebisnadiimide,N,N′-4,4-biphenylenebisnadiimide,N,N′-4,4-(3,3-dimethylbiphenylene)bisnadiimide,N,N′-4,4-(3,3-dimethyldiphenylmethane)bisnadiimide,N,N′-4,4-(3,3-diethyldiphenylmethane)bisnadiimide,N,N″-4,4-diphenylmethanebisnadiimide,N,N′-4,4-diphenylpropane-bisnadiimide,N,N′-4,4-diphenyletherbisnadiimide,N,N′-4,4-diphenylsulfonebisnadiimide,2,2-bis(4-(4-nadiimido-phenoxy)phenyl)propane,2,2-bis(3-s-butyl-3,4-(4-nadi-imidophenoxy)phenyl)propane,1,1-bis(4-(4-nadiimido-phenoxy)phenyl)decane,4,4′-cyclohexylidene-bis(1-(4-nadi-imidophenoxy)phenoxy)-2-cyclohexylbenzene,2,2-bis(4-(4-nadiimidophenoxy)phenyl)hexafluoropropane, etc., which maybe used singly or in combination of two or more in admixture.

When the above-mentioned radical polymerizable compound is used, apolymerization initiator is used. As the polymerization initiator, it isnot specifically limited so long as it is a compound which generates aradical by heat or light, and there may be mentioned a peroxide, an azocompound, etc. They are optionally selected in view of the desiredconnection temperature, connection time, preservation stability, etc.,and in the points of high reactivity and preservation stability, anorganic peroxide having a temperature of a half-life 10 hours of 40° C.or higher and a temperature of a half-life 1 minute of 180° C. or loweris preferred, and particularly preferably an organic peroxide having atemperature of a half-life 10 hours of 50° C. or higher and atemperature of a half-life 1 minute of 170° C. or lower. When theconnection time is made 10 second, a formulation amount of the curingagent to obtain a sufficient reactivity is preferably 1 to 20% byweight, particularly preferably 2 to 15% by weight based on the totalamount of the adhesive composition. Specific examples of the organicperoxide to be used in the present invention may be selected from diacylperoxide, peroxydicarbonate, peroxy ester, peroxy ketal, dialkylperoxide, hydroperoxide, silylperoxide, etc. Of these, peroxy ester,dialkyl peroxide, hydroperoxide and silylperoxide are particularlypreferably used since they contain a chlorine ion or an organic acid inthe polymerization initiator is 5,000 ppm or lower whereby an amount ofan organic acid generated after decomposition by heating is a little sothat corrosion of a connecting terminal of a circuit member can berestrained.

As the diacylperoxide, there may be mentioned, for example, isobutylperoxide, 2,4-dichlorobenzoyl peroxide, 3,5,5-trimethylhexanoylperoxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide,succinic peroxide, benzoyl-peroxytoluene, benzoyl peroxide, etc.

As the peroxydicarbonate, there may be mentioned, for example,di-n-propylperoxydicarbonate, diisopropylperoxy-dicarbonate,bis(4-t-butylcyclohexyl)peroxydicarbonate,di-2-ethoxymethoxyperoxydicarbonate, di(2-ethylexylperoxy)-dicarbonate,dimethoxybutylperoxydicarbonate,di(3-methyl-3-methoxybutylperoxy)dicarbonate, etc.

As the peroxy ester, there may be mentioned, for example,cumylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneo-decanoate,1-cyclohexyl-1-methylethylperoxyneodecanoate, t-hexylperoxyneodecanoate,t-butylperoxypivalate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanonate,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane,1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanonate,t-hexylperoxy-2-ethylhexanonate, t-butylperoxy-2-ethylhexanonate,t-butylperoxyisobutyrate, 1,1-bis(t-butylperoxy)cyclohexane,t-hexylperoxyisopropyl monocarbonate,t-butylperoxy-3,5,5-trimethylhexanonate, t-butylperoxylaurate,2,5-dimethyl-2,5-di(m-toluoylperoxy)hexane, t-butylperoxyisopropylmonocarbonate, t-butylperoxy-2-ethylhexyl monocarbonate,t-hexylperoxybenzoate, t-butylperoxyacetate, etc.

As the peroxy ketal, there may be mentioned, for example,1,1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-hexylperoxy)cyclohexane,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-(t-butylperoxy)cyclododecane, 2,2-bis(t-butylperoxy)decane, etc.

As the dialkyl peroxide, there may be mentioned, for example,α,α′-bis(t-butylperoxy)diisopropylbenzene, dicumyl-peroxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumylperoxide, etc.

As the hydroperoxide, there may be mentioned, for example,diisopropylbenzene hydroperoxide, cumene hydroperoxide, etc.

As the silyl peroxide, there may be mentioned, for example,t-butyltrimethylsilyl peroxide, bis(t-butyl)dimethylsilyl peroxide,t-butyltrivinylsilyl peroxide, bis(t-butyl)divinylsilyl peroxide,tris(t-butyl)vinylsilyl peroxide, t-butyltriallylsillyl peroxide,bis(t-butyl)diallylsillyl peroxide, tris(t-butyl)allylsillyl peroxide,etc.

These organic peroxides are preferably those containing amounts of achlorine ion or an organic acid in the curing agent or in the organicperoxide of 5,000 ppm or less to restrain corrosion of a connectionterminal of a circuit member or corrosion of a circuit electrode, andthose generating less amount of an organic acid after decomposition byheating are more preferred. Also, those having a weight retaining ratioafter allowing to stand under opening at a room temperature (25° C.) anda normal pressure for 24 hours of 20% by weight or more since stabilityof the prepared circuit connecting material is improved. These organicperoxides may be used singly or in combination of two or more.

These free radical generators may be used alone or in combination of twoor more in admixture, and a decomposition accelerator or a retarder,etc., may be used in combination.

Also, when these curing agents are encapsulated in a polymer substancesuch as a polyurethane resin, a polyester resin, etc. to formmicrocapsules, they are preferably used since a usable time can beelongated.

As the thermosetting resin other than the radical polymerization, theremay be mentioned an epoxy resin. As the epoxy resin, there may bementioned, for example, a bisphenol A type epoxy resin, a bisphenol Ftype epoxy resin, a bisphenol S type epoxy resin, a phenol novolak typeepoxy resin, a cresol novolak type epoxy resin, a bisphenol A novolakepoxy resin, a bisphenol F novolak epoxy resin, an alicyclic epoxyresin, a glycidyl ester type epoxy resin, a glycidyl amine type epoxyresin, a hydantoin type epoxy resin, an isocyanurate type epoxy resin,an aliphatic chain-state epoxy resin, etc., and these epoxy resins maybe halogenated or hydrogenated. These epoxy resin may be used alone orin combination of two or more kinds in admixture.

As a curing agent of the above-mentioned epoxy resin, there may bementioned a curing agent which has been generally used, for example, anamine, a phenol, an acid anhydride, an imidazole, a dicyanediamide, etc.Further, a tertiary amine or an organic phosphor type compound which hasbeen generally used as a curing accelerator may be optionally used.

Also, as a method for reacting the epoxy resin, other than using theabove-mentioned curing agents, a cation polymerization may be carriedout by using a sulfonium salt, an iodonium salt, etc.

In the adhesive for connecting a circuit of the present invention, toprovide a film-forming property, adhesive property or stress relaxingproperty at the time of curing, a polymer component such as apolyvinylbutyral resin, a polyvinylformal resin, a polyester resin, apolyamide resin, a polyimide resin, a xylene resin, a phenoxy resin, apolyurethane resin, a urea resin, etc., may be used. These polymercomponents preferably have a weight average molecular weight of 10,000to 10,000,000. Also, these resins may be modified by at least oneradical polymerizable functional group(s). When the resin is somodified, heat resistance of the resulting material is improved.Moreover, when these resins contain at least one carboxyl group(s), sucha resin can be used as the carboxyl group-containing compound of thepresent invention. A formulation amount of the polymer component is 2 to80% by weight, preferably 5 to 70% by weight, particularly preferably 10to 60% by weight based on the total amount of the adhesive composition.If the amount is less than 2% by weight, stress relaxation or adhesiveforce is insufficient, while if it exceeds 80% by weight, flowability islowered.

To the adhesive for connecting a circuit of the present invention may beoptionally added a filler, a softening agent, a promoter, an agingpreventive agent, a coloring agent, a flame retardant, a coupling agent,etc.

Even when the adhesive for connecting a circuit of the present inventiondoes not contain conductive particles, connection can be obtained whenthe opposed electrodes are directly contacted to each other at the timeof connection, and when it contains conductive particles, connection canbe more stably established. As the conductive particles, there may beused metal particles such as Au, Ag, Ni, Cu and solder, or carbon;particles in which non-conductive particles such as glass, ceramic,plastic, etc., are covered by noble metal such as Au, Ag, Pt, etc. Whenmetal particles are used, to prevent from oxidation at the surface ofthe particle, those coated by noble metal are preferably used. Of theabove-mentioned conductive particles, particles using plastic as nucleicmaterial and coated by Au, Ag, etc., or heat fusible metal particles aredeformed by heating under pressure at the time of connection wherebycontacting surface area is increased and reliability is improved. Athickness of the coating layer of the noble metal is generally 100 Å ormore, preferably 300 Å or more whereby good connection can be obtained.Also, particles in which the above-mentioned conductive particles arecovered by an insulating resin may be used. The conductive particles arepreferably used in an amount of 0.1 to 30% by volume, more preferably0.1 to 10% by volume based on 100% by volume of the adhesive componentoptionally depending on the purposes.

Also, in the first embodiment of the present invention, the adhesive forconnecting a circuit may be constituted by a multi-layered constitutioncomprising two or more layers having a glass transition temperature (Tg)of the cured product 5° C. or more different from each other.

Moreover, in the second embodiment, it is preferred to contain acompound having an acid equivalent of 5 to 500 (KOH mg/g) in at leastone of the first adhesive layer and the second adhesive layer.

As a substrate to be adhered by using the adhesive for connecting acircuit of the present invention, it is not particularly limited so longas that on which electrodes for which an electrical connection isrequired are formed, and there may be mentioned, for example, a glass orplastic substrate on which electrodes are formed by ITO, etc., used fora liquid crystal display device, a printed wiring board, a ceramicwiring board, a flexible wiring board, a semiconductor silicon chip,etc., and these substrates are used in combination, if necessary.

When connection is carried out by using the above-mentioned substrates,as the adhesive for connecting a circuit in the second embodiment of thepresent invention, the first adhesive layer having a higher Tg ispreferably provided to the substrate side having a higher modulus ofelasticity. According to this constitution, occurrence of lifting can bereduced.

The conditions to effect connection are not particularly limited, and,for example, it is carried out at a connection temperature of 90 to 250°C. and a connection time of 1 second to 10 minutes, which can beoptionally selected depending on the uses, a kind of an adhesive or asubstrate to be used, etc. If necessary, a post-curing treatment may becarried out. Also, the connection is carried out under heating andpressure, and, if necessary, an energy other than heat, such as light,an ultrasonic wave, an electromagnetic wave, etc. may be used.

EXAMPLES

In the following, the present invention is explained more specificallyby referring to Examples, but the scope of the present invention is notlimited by these Examples.

The respective components are formulated with the following formulation,and coated on a PET (polyethylene-terephthalate) film having a thicknessof 50 μm one surface of which is subjected to surface treatment by usinga simple and easy coating machine (manufactured by Tester Sangyo K.K.,Japan) and dried with hot air at 70° C. for 5 minutes to prepare a film.

(Synthesis of Urethane Acrylate)

A composition comprising 400 parts by weight of polycaprolactone diolhaving a weight average molecular weight (Mw) of 800, 131 parts byweight of 2-hydroxypropyl acrylate, 0.5 part by weight of dibutyl tindilaurate as a catalyst, and 1.0 part by weight of hydroquinonemonomethyl ether as a polymerization inhibitor was mixed by heating to50° C. while stirring. Then, 222 parts by weight of isophoronediisocyanate was added dropwise to the mixture and the resulting mixturewas heated to 80° C. while stirring to carry out a reaction for formingurethane. After confirming that a reaction rate of NCO became 99% orhigher, the reaction temperature was lowered to obtain an urethaneacrylate.

As a radical polymerizable substance, the above-mentioned urethaneacrylate was used. Also, as a film-forming material, a carboxylicacid-modified butyral resin (6000EP; trade name, available from DenkiKagaku Kogyo K.K., Japan, an acid equivalent: 250 (KOH mg/g)) and aphenoxy resin (PKHC; trade name, available from Union Carbide, Co., aweight average molecular weight: 45,000) were used.

As a curing agent which generates a free radical by heating, a 50% byweight DOP (dioctylphthalate) solution oft-hexylperoxy-2-ethylhexanonate was used.

As conductive particles, conductive particles having an average particlesize of 4 μm wherein on the surface of a particle comprising polystyreneas a nucleus, a nickel layer having a thickness of 0.2 μm was provided,and a gold layer having a thickness of 0.04 μm was further provided onthe surface of the nickel layer were prepared and used.

Example 1

The respective components were formulated with a solid weight ratio, 20g of the carboxylic acid-modified butyral resin (as a solid component),30 g of the phenoxy resin (as a solid component), 49 g of the urethaneacrylate, 1 g of a phosphoric acid ester type acrylate (available fromKyoeisha Yushi K.K., trade name: P2M), and 5 g oft-hexylperoxy-2-ethylhexanonate (10 g as a DOP solution), and theconductive particles are further formulated and dispersed in an amountof 3% by volume, coated and dried to obtain a circuit connectingmaterial having an adhesive layer with a thickness of 8 μm.

(Preparation of Circuit Connecting Structure)

The above-obtained circuit connecting material was slit with a width of1.5 mm and a piece thereof was tentatively connected on a glasssubstrate on which an ITO was formed as an electrode under theconditions of 80° C., 5 seconds and 1 MPa. The PET substrate was peeledoff and an electrode(s) of TCP was placed thereon by positioning andconnected under the conditions of 150° C., 20 seconds and 4 MPa.

Example 2

The respective components were formulated with a solid weight ratio, 30g of the carboxylic acid-modified butyral resin (as a solid component),30 g of the phenoxy resin (as a solid component), 39 g of the urethaneacrylate, 1 g of a phosphoric acid ester type acrylate (available fromKyoeisha Yushi K.K., trade name: P2M), and 5 g oft-hexylperoxy-2-ethylhexanonate (10 g as a DOP solution), and theconductive particles are further formulated and dispersed in an amountof 3% by volume, coated and dried to obtain a circuit connectingmaterial having an adhesive layer with a thickness of 8 μm.

(Preparation of Circuit Connecting Structure)

The above-obtained circuit connecting material was slit with a width of1.5 mm and a piece thereof was tentatively connected on a glasssubstrate on which an ITO was formed as an electrode under theconditions of 80° C., 5 seconds and 1 MPa. The PET substrate was peeledoff and an electrode(s) of TCP was placed thereon by positioning andconnected under the conditions of 150° C., 20 seconds and 4 MPa.

Example 3

The respective components were formulated with a solid weight ratio, 10g of the carboxylic acid-modified butyral resin (as a solid component),35 g of the phenoxy resin (as a solid component), 54 g of the urethaneacrylate, 1 g of a phosphoric acid ester type acrylate (available fromKyoeisha Yushi K.K., trade name: P2M), and 5 g oft-hexylperoxy-2-ethylhexanonate (10 g as a DOP solution), and theconductive particles are further formulated and dispersed in an amountof 3% by volume, coated and dried to obtain a circuit connectingmaterial having an adhesive layer with a thickness of 8 μm.

(Preparation of Circuit Connecting Structure)

The above-obtained circuit connecting material was slit with a width of1.5 mm and a piece thereof was tentatively connected on a glasssubstrate on which an ITO was formed as an electrode under theconditions of 80° C., 5 seconds and 1 MPa. The PET substrate was peeledoff and an electrode(s) of TCP was placed thereon by positioning andconnected under the conditions of 150° C., 20 seconds and 4 MPa.

Comparative Example 1

The respective components were formulated with a solid weight ratio, 45g of the phenoxy resin (as a solid component), 54 g of the urethaneacrylate, 1 g of a phosphoric acid ester type acrylate (available fromKyoeisha Yushi K.K., trade name: P2M), and 5 g oft-hexylperoxy-2-ethylhexanonate (10 g as a DOP solution), and theconductive particles are further formulated and dispersed in an amountof 3% by volume, coated and dried to obtain a circuit connectingmaterial having an adhesive layer with a thickness of 8 μm.

(Preparation of Circuit Connecting Structure)

The above-obtained circuit connecting material was slit with a width of1.5 mm and a piece thereof was tentatively connected on a glasssubstrate on which an ITO was formed as an electrode under theconditions of 80° C., 5 seconds and 1 MPa. The PET substrate was peeledoff and an electrode(s) of TCP was placed thereon by positioning andconnected under the conditions of 150° C., 20 seconds and 4 MPa.

(Characteristics Evaluating Method)

(1) Connection resistance: By using Multimeter TR6848 manufactured byK.K. Advantest, Japan, a resistance between circuits adjacent to eachother was measured with a constant electric current of 1 mA.

(2) Adhesion strength: According to JIS Z-0237, it was measured by usingStrograph E-S type manufactured by K.K. Toyo Seiki Seisakusho, Japan,with 90° peel.

(3) Observation at connected portion: Presence or absence of peeling andbubble at the connected portion was observed by a metallic microscope.

(4) Reliability evaluation: With regard to the above-mentionedconnecting resistance and adhesive force, high temperature and highhumidity test was carried out under the conditions of 80° C. and 95% RH(relative humidity) for 240 hours, and then, the sample was taken outand the above items (1) to (3) were tested.The measured results were shown in Table 1.

TABLE 1 Connection Adhesive force Appearance at resistance (Ω) (N/m)connected portion Humidity Humidity Humidity resistance resistanceresistance test test test after 240 after 240 after 240 Items Initialhours Initial hours Initial hours Example 1 2 2.2 1150 1000 Good GoodExample 2 2.2 2.3 1290 1180 Good Good Example 3 2.1 2.4 1030 1030 GoodGood Comparative 2.6 5.3 760 350 Good Lifting example 1 occurred

In Examples 1 to 3 of the present invention, good characteristics areshown in either of the connection resistance, adhesive force andappearance at the connected portion, and even after the humidityresistance test, good reliabilities are shown. To the contrary, inComparative example 1 wherein the compound having an acid equivalent ofless than 5 (KOH mg/g) is used, an initial value of the adhesive forceis low and connection resistance after the humidity resistance test ishigh and an adhesion force also becomes weak and lifting is occurred sothat connection reliability is poor.

Example 4 First Adhesive Layer

As the radical polymerizable substance, dimethylol-tricyclodecanediacrylate and the above-mentioned urethane acrylate were used.

As a film forming material, a phenoxy resin (PKHC; trade name, availablefrom Union Carbide Co., a weight average molecular weight: 45,000) wasused.

As a curing agent which generates a free radical by heating, a 50% byweight DOP (dioctylphthalate) solution oft-hexylperoxy-2-ethylhexanonate was used.

On the surface of a particle comprising polystyrene as a nucleus, anickel layer with a thickness of 0.2 μm was provided, and a gold layerwith a thickness of 0.04 μm was further provided on the surface of thenickel layer to prepare conductive particles having an average particlesize of 4 μm.

The respective components were formulated with a solid weight ratio, 50g of the phenoxy resin (as a solid component), 30 g ofdimethyloltricyclodecane diacryalte, 19 g of the urethane acrylate, 1 gof a phosphoric acid ester type acrylate (available from Kyoeisha YushiK.K., trade name: P2M), and 5 g of t-hexylperoxy-2-ethylhexanonate (10 gas a DOP solution), and the conductive particles are further formulatedand dispersed in an amount of 3% by volume, coated and dried to obtain acircuit connecting material having an adhesive layer with a thickness of8 μm (Tg of the cured product was 110° C.)

Second Adhesive Layer

As the radical polymerizable substance, the urethane acrylate was used.

As a film forming material, a phenoxy resin (PKHC; trade name, availablefrom Union Carbide Co., a weight average molecular weight: 45,000) wasused.

As a curing agent which generates a free radical by heating, a 50% byweight DOP (dioctylphthalate) solution oft-hexylperoxy-2-ethylhexanonate was used.

On the surface of a particle comprising polystyrene as a nucleus, anickel layer with a thickness of 0.2 μm was provided, and a gold layerwith a thickness of 0.04 μm was further provided on the surface of thenickel layer to prepare conductive particles having an average particlesize of 4 μm.

The respective components were formulated with a solid weight ratio, 50g of the phenoxy resin (as a solid component), 10 g ofdimethyloltricyclodecane diacryalte, 39 g of the urethane acrylatesynthesized as mentioned above, 1 g of a phosphoric acid ester typeacrylate (available from Kyoeisha Yushi K.K., trade name: P2M), and 5 gof t-hexylperoxy-2-ethylhexanonate (10 g as a DOP solution), and theconductive particles are further formulated and dispersed in an amountof 3% by volume, coated and dried to obtain a circuit connectingmaterial having an adhesive layer with a thickness of 18 μm (Tg of thecured product was 60° C.).

The first adhesive layer and the second adhesive layer were laminated byusing a roll laminator to prepare an adhesive for connecting a circuithaving a two-layered constitution.

Example 5 First Adhesive Layer

In the same manner as in the first adhesive layer of Example 4 exceptfor changing the thickness of the adhesive layer to 12 μm, a circuitconnecting material was obtained (Tg of the cured material was 110° C.).

Second Adhesive Layer

In the same manner as in the second adhesive layer of Example 4 exceptfor changing the thickness of the adhesive layer to 15 μm, a circuitconnecting material was obtained (Tg of the cured material was 60° C.).

The first adhesive layer and the second adhesive layer were laminated byusing a roll laminator to prepare an adhesive for connecting a circuithaving a two-layered constitution.

Example 6 First Adhesive Layer

In the same manner as in the first adhesive layer of Example 4 exceptfor changing the thickness of the adhesive layer to 18 μm, a circuitconnecting material was obtained (Tg of the cured material was 110° C.)

Second Adhesive Layer

In the same manner as in the second adhesive layer of Example 4 exceptfor changing the thickness of the adhesive layer to 14 μm, a circuitconnecting material was obtained (Tg of the cured material was 60° C.).

The first adhesive layer and the second adhesive layer were laminated byusing a roll laminator to prepare an adhesive for connecting a circuithaving a two-layered constitution.

Example 7 First Adhesive Layer

As a film forming material, a phenoxy resin (PKHC; trade name, availablefrom Union Carbide Co., a weight average molecular weight: 45,000) wasused.

As a curing agent which generates a free radical by heating, a 50% byweight DOP (dioctylphthalate) solution oft-hexylperoxy-2-ethylhexanonate was used.

On the surface of a particle comprising polystyrene as a nucleus, anickel layer with a thickness of 0.2 μm was provided, and a gold layerwith a thickness of 0.04 μm was further provided on the surface of thenickel layer to prepare conductive particles having an average particlesize of 4 μm.

The respective components were formulated with a solid weight ratio, 40g of the phenoxy resin (as a solid component), 20 g ofdimethyloltricyclodecane diacryalte, 39 g of the urethane acrylate, 1 gof a phosphoric acid ester type acrylate (available from Kyoeisha YushiK.K., trade name: P2M), and 5 g of t-hexylperoxy-2-ethylhexanonate (10 gas a DOP solution), and the conductive particles are further formulatedand dispersed in an amount of 3% by volume, coated and dried to obtain acircuit connecting material having an adhesive layer with a thickness of8 μm (Tg of the cured product was 68° C.).

Second Adhesive Layer

As the radical polymerizable substance, the urethane acrylate was used.

As a film forming material, a phenoxy resin (PKHC; trade name, availablefrom Union Carbide Co., a weight average molecular weight: 45,000) and acarboxylic acid-modified butyral resin (6000EP; trade name, availablefrom Denki Kagaku Kogyo K.K., Japan, an acid equivalent: 250 (KOH mg/g))were used.

As a curing agent which generates a free radical by heating, a 50% byweight DOP (dioctylphthalate) solution oft-hexylperoxy-2-ethylhexanonate was used.

On the surface of a particle comprising polystyrene as a nucleus, anickel layer with a thickness of 0.2 μm was provided, and a gold layerwith a thickness of 0.04 μm was further provided on the surface of thenickel layer to prepare conductive particles having an average particlesize of 4 μm.

The respective components were formulated with a solid weight ratio, 30g of the phenoxy resin (as a solid component), 20 g of the carboxylicacid-modified butyral resin (as a solid component), 10 g ofdimethyloltricyclodecane diacryalte, 39 g of the urethane acrylatesynthesized as mentioned above, 1 g of a phosphoric acid ester typeacrylate (available from Kyoeisha Yushi K.K., trade name: P2M), and 5 gof t-hexylperoxy-2-ethylhexanonate (10 g as a DOP solution), and theconductive particles are further formulated and dispersed in an amountof 3% by volume, coated and dried to obtain a circuit connectingmaterial having an adhesive layer with a thickness of 18 μm (Tg of thecured product was 52° C.).

The first adhesive layer and the second adhesive layer were laminated byusing a roll laminator to prepare an adhesive for connecting a circuithaving a two-layered constitution.

Comparative Example 2

A circuit connecting material was obtained by using the first adhesivelayer alone of Example 4 and making the thickness of the adhesive layer25 μm (Tg of the cured product was 110° C.)

Comparative Example 3

A circuit connecting material was obtained by using the second adhesivelayer alone of Example 4 and making the thickness of the adhesive layer25 μm (Tg of the cured product was 60° C.)

(Preparation of Connecting Material)

The above-obtained adhesive for connecting a circuit with thetwo-layered constitution was slit with a width of 1.5 mm and a piecethereof was tentatively connected on a glass substrate on which an ITOwas formed as an electrode (at the substrate side having a highermodulus of elasticity) under the conditions of 80° C., 5 seconds and 1MPa. Then, the PET substrate was peeled off and positioning of anelectrode of ITO and an electrode of TCP was carried out and connectedunder the conditions of 140° C., 20 seconds and 4 MPa.

Also, as Reference example of the present invention, the adhesive ofExample 4 with the two-layered constitution was so provided that thesecond adhesive layer having a lower Tg is positioned at the glass side,and connection was carried out with the same conditions. Also, theadhesives for connecting a circuit prepared in Comparative examples 2and 3 were treated in the same manner as mentioned above.

(Characteristics Evaluating Method)

In the same manner as in Examples 1 to 3 and Comparative example 1, thecharacteristics were measured.

The results of the characteristics measured were shown in Table 2.

TABLE 2 Connection Adhesive force Appearance at resistance (Ω) (N/m)connected portion Humidity Humidity Humidity resistance resistanceresistance test test test after 240 after 240 after 240 Items Initialhours Initial hours Initial hours Example 4 2.1 2.3 1200 1100 Good GoodExample 5 2.2 2.5 1050 1000 Good Good Example 6 2.4 2.8 1250 1180 GoodGood Example 7 2.5 2.9 1000 970 Good Good Comparative 2.2 2.2 1100 950Good Lifting example 2 occurred Comparative 2.2 10 1250 450 Good Liftingexample 3 occurred Reference 2.1 4.6 1100 650 Good Lifting exampleoccurred

In Examples 4 to 7 of the present invention, good characteristics areshown in either of the connection resistance, adhesive force andappearance at the connected portion, and even after the humidityresistance test, good reliabilities are shown.

To the contrary, in Comparative examples 2 and 3 with a single layerconstitution, in Comparative example 2 wherein Tg is 110° C., there isno change in connection resistance and is good, but the adhesive forceis slightly lowered and lifting is generated. Also, in Comparativeexample 3 having a low Tg of 60° C., increase in connection resistanceafter 240 hours of the humidity resistance test is observed, theadhesive force is lowered and lifting is also generated.

On the other hand, when the second adhesive layer having a low Tg isprovided at the glass substrate side, lifting may sometimes occur sothat, in the present invention, it is preferred to provide the firstadhesive layer having a high Td is provided at the glass substrate side.

Utilizability in Industry

According to the first embodiment of the present invention, adhesiveforces at an initial stage and after the humidity resistance test can bemade high, and an adhesive for connecting a circuit which can accomplishlowering in the connection temperature and shortening of the connectiontime and a circuit connecting structure using the same can be provided.

Also, in the adhesive for connecting a circuit, and a circuit connectingmethod and a circuit connecting structure using the same according tothe second embodiment of the present invention, it is possible to carryout the connection at 140° C. for 20 seconds which corresponds tolowering in the connection temperature and shortening of the connectiontime. And after the humidity resistance test after the connection, nolifting which is peeling is generated so that a circuit connectingstructure showing an excellent connection reliability can be provided.

1. An adhesive structure which comprises an adhesive for connecting acircuit to be interposed between substrates having circuit electrodesthereon opposed to each other and to electrically connect the circuitelectrodes on the substrates opposed to each other in the pressurizingdirection under pressure, wherein said adhesive contains a firstadhesive layer and a second adhesive layer in a thickness direction, aglass transition temperature of the first adhesive layer after pressureconnection is higher than the glass transition temperature of the secondadhesive layer after pressure connection, and each of the first adhesivelayer and the second adhesive layer contains (1) urethane (meth)acrylateand (2) a radical polymerizable substance having a phosphate structureas radical polymerizable substances.
 2. The adhesive structure accordingto claim 1, wherein Tg of the first adhesive layer after connection is50° to 200° C., Tg of the second adhesive layer after connection is 40°to 100° C., and Tg of the first adhesive layer is not lower than 5° C.of Tg of the second adhesive layer after connection.
 3. The adhesivestructure according to claim 2, wherein conductive particles arecontained in at least one of the first adhesive layer and the secondadhesive layer.
 4. The adhesive structure according to claim 3, whereina ratio of the thicknesses of the first adhesive layer and the secondadhesive layer is a thickness of the first adhesive layer/a thickness ofthe second adhesive layer=0.3 to 3.0.
 5. The adhesive structureaccording to claim 4, wherein a compound having an acid equivalent of 5to 500 KOH mg/g is contained in at least one of the first adhesive layerand the second adhesive layer.
 6. A circuit connecting method, whichcomprises interposing the adhesive structure according to claim 5between substrates having circuit electrodes opposed to each other andelectrically connecting the electrodes in the pressurizing direction bypressurizing the substrates, wherein said adhesive comprises the firstadhesive layer and the second adhesive layer, Tg of the first adhesivelayer after pressure connection is higher than Tg of the second adhesivelayer after pressure connection, and the first adhesive layer having ahigher Tg is provided and connected to the substrate side having ahigher modulus of elasticity among the substrates having circuitelectrodes opposed to each other.
 7. A connecting structure whichcomprises the adhesive structure according to claim 5 being interposedbetween substrates having circuit electrodes opposed to each other andthe electrodes being electrically connected in the pressurizingdirection by pressurizing the substrates, wherein said adhesivecomprises the first adhesive layer and the second adhesive layer, Tg ofthe first adhesive layer after pressure connection is higher than Tg ofthe second adhesive layer after pressure connection, and the firstadhesive layer having a higher modulus of elasticity among thesubstrates having circuit electrodes opposed to each other.
 8. Theadhesive structure according to claim 1, wherein conductive particlesare contained in at least one of the first adhesive layer and the secondadhesive layer.
 9. The adhesive structure according to claim 1, whereina ratio of the thicknesses of the first adhesive layer and the secondadhesive layer is a thickness of the first adhesive layer/a thickness ofthe second adhesive layer=0.3 to 3.0.
 10. The adhesive structureaccording to claim 1, wherein a compound having an acid equivalent of 5to 500 KOH mg/g is contained in at least one of the first adhesive layerand the second adhesive layer.
 11. A circuit connecting method, whichcomprises interposing the adhesive structure according to claim 1between substrates having circuit electrodes opposed to each other andelectrically connecting the electrodes in the pressurizing direction bypressurizing the substrates, wherein said adhesive comprises the firstadhesive layer and the second adhesive layer, Tg of the first adhesivelayer after pressure connection is higher than Tg of the second adhesivelayer after pressure connection, and the first adhesive layer having ahigher Tg is provided and connected to the substrate side having ahigher modulus of elasticity among the substrates having circuitelectrodes opposed to each other.
 12. A connecting structure whichcomprises the adhesive structure according to claim 1 being interposedbetween substrates having circuit electrodes opposed to each other andthe electrodes being electrically connected in the pressurizingdirection by pressurizing the substrates, wherein said adhesivecomprises the first adhesive layer and the second adhesive layer, Tg ofthe first adhesive layer after pressure connection is higher than Tg ofthe second adhesive layer after pressure connection, and the firstadhesive layer having a higher Tg is provided and connected to thesubstrate side having a higher modulus of elasticity among thesubstrates having circuit electrodes opposed to each other.